A known wire electrode member and apparatus for electrical discharge machining is described in U.S. Pat. No. 4,287,404 wherein the electrically conductive metal wire is provided with an active surface comprising at least 50 percent by weight of a metal or alloy selected from a group consisting of zinc, cadmium, tin, lead, antimony and bismuth. In the preferred apparatus, said active surface coating is provided by electrolytic plating on the exterior surface of a conventional metal wire in a continuous manner during the machining operation. Such continuous replenishment of the active surface while the workpiece is being machined understandably renders the equipment more complex to build and operate. Cutting speeds for said prior art wire electrode member is said to be optimum when the core metal is copper or brass since a steel core member is said to require coating with copper or silver for improved electrical conductance. Accordingly, desirable mechanical strength for this electrode member is obtained at some sacrifice in the electrical conductance unless added costs are incurred with utilization of the disclosed higher conductivity inner layer. A low vaporization temperature for the active surface coating on said prior art electrode member is also said to be needed in order to avoid rupturing said electrode member in the machining zone.
It remains desirable, therefore, to overcome the above mentioned drawbacks with an electrode member suitable for electrical discharge machining as well as increase the cutting speeds in said type machining operation.
A further desirable objective is to simplify the process and equipment needed to carry out electrical discharge machining insofar as attributable to the wire electrode member being utilized.
These and other objectives of the present invention will be apparent from the following detailed description.